The present invention concerns the use of inhibitors for the treatment and/or prophylaxis of diseases which are the consequence of increased receptor tyrosine kinase activity, particularly cancer. The use is particularly directed towards inhibition or lowering of the overexpression and/or altered activity of receptor tyrosine kinases (RTKs). In particular, this altered activity of receptor tyrosine kinase can be triggered by a mutation of FGFR-4, wherein this mutation is in particular a point mutation in the transmembrane domain of FGFR-4 and leads to the exchange of a hydrophobic amino acid for a hydrophilic amino acid. The invention further concerns the use of the inhibitors of FGFR kinases, particularly for the treatment and/or prophylaxis of cancer. Furthermore, the invention concerns a mutated FGFR-4, which leads to overexpression and/or altered activity in cells. Finally, the invention concerns a DNA and RNA sequence of a mutated FGFR-4 molecule. Finally, in addition the invention concerns a pharmaceutical composition, containing the inhibitor as described above and, further, a diagnostic and screening procedure.
Cell growth is a carefully regulated process dependent on the specific needs of an organism. In a young organism, the cell division rate exceeds the cell death rate, which leads to an increase in the size of the organism. In an adult organism, the new formation of cells and cell death are balanced so that a “steady state” arises. In rare cases, however, the control of cell multiplication breaks down and the cells begin to grow and to divide, although no specific need for a higher number of cells of this type exists in the organism. This uncontrolled cell growth is the cause of cancer. Factors that can provoke the uncontrolled cell growth, some-times associated with metastasis formation, are often of a chemical nature, but can also be of a physical nature, such as for example radioactive radiation. Another cause of the triggering of cancer are genetic peculiarities or mutations in a certain organism, which sooner or later lead to the cells degenerating.
Up to now, it has still not been possible satisfactorily to elucidate the processes which control normal growth and differentiation, for example in the breast. In addition to hormonal control, there is also a complex network of different, locally generated growth factors which intervene in the development of the mammary cells. The precise causes of the occurrence of cancer in mammary cells are as unclear and unknown as they are diverse, as is also the case with other cells. Alterations in oncogenes and tumour suppressor genes appear to play an important part in breast cancer carcinogenesis. In addition, reinforced stimulation by regulatory factors which arise in genetically altered cells can lead to increased progression of cell growth.
At present, essentially two alternatives are available for the treatment of cancer. Either the cancer cells are successfully removed from the diseased organism completely by a surgical intervention, or attempts are made to render the degenerated cells in the organism harmless, for example by administration of medicaments (chemotherapy) or by physical therapeutic procedures, such as irradiation.
In chemotherapy, medicaments are often used which in some form intervene in the DNA metabolism and damage rapidly growing cells, which have to produce higher DNA metabolic capacity, more strongly than cells which are dividing slowly or not at all. However, a severe disadvantage of many chemotherapeutic drugs is the low specificity of the active substance used, as a result of which healthy cells are also damaged during the chemotherapy. This low specificity of the active substances further requires that their dosage must in each case be such that as few as possible healthy cells are damaged, with simultaneous killing of the cancer cells. This is often not possible, and the cancer patient dies because of the ever further spreading cancer cells, which in the final stages cause the failure of vital functions.
It is assumed that the overexpression and/or altered activity of certain growth factor receptors contribute to the intensified growth of many neoplasms, including breast cancer. For example, the overexpression of EGFR, i.e. epidermal factor receptor, or ERB B-2 receptor in breast tumours has been linked with a poor prognosis. FGF (historically: fibroblast growth factor) proteins could also be involved in the development of cancer in breast glands or of other cancer; however the results in this regard are contradictory or are inconclusive.
The FGFs constitute a large family of peptide regulatory factors, of which 9 members are so far known. Eight of these have been well characterised in man (Basilico and Moscatelli, 1992; Coulier et al., 1993). The FGFs operate via high-affinity tyrosine kinase receptors, which are coded for by at least four different genes. Further, the FGFs are multifunctional, regulatory peptides which could have an effect not only on tumorigenesis but could also play a major part in cardiovascular diseases, reconstruction after tissue injury, neurobiology and embryonic development. The acidic and basic FGFs (aFGF and bFGF) were the first and are the best characterised members of the family. In vivo it could for example be shown that FGFs are involved in mesodermal induction in embryogenesis (Slack et al., 1987; Kimelman et al., 1988), and also involvement in angiogenesis (Thomas et al., 1985; Thompson et al., 1989; Folkmann and Klagsbrun, 1987).
For the corresponding receptors (FGFRs), four similar genes coding for them have been identified. These genes code for structurally related proteins with an extracellular domain which consists of three immunoglobulin loops and an acid portion, a hydrophobic trans-membrane domain and an intracellular domain, which incorporates a tyrosine kinase activity. For two of these genes, FGFR-1 and FGFR-2, it could be shown that they have multiple transcripts, which arise by alternative splicing (Givol and Yayon, 1992 and Johnson and Williams, 1993). Splice variants which arise from these genes differ with respect to the number of immunoglobulin-like domains in the extracellular region of the receptor and in the sequence for the second half of the third immunoglobulin domain, which can arise from alternative exons. In addition, transmembrane and juxtamembrane shortenings or deletions can arise, which can generate secreted or kinase-inactive protein products.
For FGFR-3, it was possible to find alternative transcripts and corresponding isoforms, but for FGFR-4 there is only a single known protein product. Because of the large number of FGFR genes and transcripts and the lack in many protein products of a specificity for defined FGFs, it is difficult to determine the action of a specific ligand on a specific receptor. Hence, correlations between specific FGF receptors and defined diseases can only be established with great difficulty, let alone a correlation of a particular mechanism of action of a defined receptor with a disease. Accordingly, it is difficult effectively to treat diseases, especially the complex disease picture cancer, utilising the FGFRs.